Solenoid operated fluid control valves are used throughout industry to perform a wide variety of functions. Several types of fluid control valves are available including relief valves, pressure regulating valves, ON/OFF valves and directional or shift valves.
Directional or shift valves are generally used to control the communication of pressurized fluid to one of two working ports. Generally, the valve includes a spool which may be spring or pressure centered. In the centered position, pressure at an inlet to the valve is either blocked or communicated to tank. When the spool is shifted from the center position to one of its shifted positions, pressurized fluid at the inlet is communicated to one, of the working ports, depending on the direction the spool is shifted.
Some of the currently available shift valves include a spring centered spool that is directly operated by large solenoids. In these valves, large forces must be generated by the solenoids to overcome the spring generated centering force in order to move the spool. These types of valves require substantial electrical power to energize the solenoids. Relays are generally needed to control the application of power to the solenoids.
Pilot type valves are also available which utilize low power solenoids to achieve shifting of the spool. In these pilot valves, only relatively small flow rates are accommodated and, in general, are used to control discrete valves that are separately mounted from the pilot valve.
In some currently available valves of this type, a pilot valve and a main spool are mounted in the same housing. The main spool is shifted by pilot pressure that is controlled by a solenoid operated pilot spool. The pilot spool is shifted from a center position to one of two shifted positions by actuating one of the solenoids. Pilot pressure is then directed to the main spool where it is applied to an effective pressure area on the spool. The applied pilot pressure creates a force on the spool to shift it from the center position to one of the operating positions activated.
Currently available valves of this type can be large and cumbersome. In order to service or repair many of these types of valves, partial disassembly is required in order to separate the pilot section from the main flow section. At least some of these valves require several mounting fasteners and complex gasketing in order to attach and seal the valve to the hydraulic system or hydraulic component. Repairs and replacements can therefore be costly as well as time consuming.
In some currently available direction control valves, forces needed to shift the pilot spool from its center position can be substantial. As a result, the solenoids used in these types of valves require substantial currents for operation. Many electronic controls, on the other hand, are able to provide only relatively small amounts of current, i.e., less than 1 amp to operate control devices. As a result, at least some directional valves now on the market require a separate relay to operate the solenoid coils, with the relay in turn controlled by the electronic control circuit. It is desirable to provide a directional valve that is both easy to maintain and replace and which can be directly energized by the output drive currents available from conventional electronic controls.